1. Field of the Invention
This invention relates to the use of certain enzyme compositions which can be incorporated in the ingredients used to prepare baked goods to improve softness and retard staling of the products.
2. Description of the Prior Art
The phenomenon of staling of baked goods is not completely understood. Staling is usually related to the retrogradation of starch, or the association of starch molecules to form areas of crystallinity which result in an increase in firmness of the product with the passage of time. Staling is of considerable economic importance to wholesale bakeries since it limits the shelf life of baked goods in retail outlets to about 3 or 4 days, plus several additional days in the home of the consumer after purchase. The short shelf life of the baked goods has required wholesale bakeries to have separate distribution systems that operate independently of the usual channels for packaged food distribution. In addition, the market area of a bakery is generally limited by the maximum radius the distribution system can cover within 24 hours.
Cereal chemists and bakery technologists have found that various chemical emulsifiers have some influence in extending the shelf life of baked goods, such as bread. However, chemical emulsifiers are only partially effective in reducing bread staling. Monoglycerides and other emulsifiers have been added to bread to improve its softness. Although these emulsifiers produce a softer bread, they have little influence in reducing the rate of bread staling. The term "baked goods" also connotes application to such products as rolls, muffins, biscuits, donuts, crackers and cake.
Enzymes derived from bacterial sources have been used or suggested for use in baked goods for the specific purpose of inhibiting staling.
"Heat stable bacterial alpha-amylase" enzyme as the term is used in the baking and enzyme industries, most often refers to enzymes made from Bacillus subtilis, which are used to inhibit staling. The Bacillus subtilis enzyme has a Phadebas activity for baking purposes above 100% at temperatures of about 60.degree. to 80.degree. C. at a pH of about 6.2, and retains greater than 50% of its Phadebas activity at temperatures approaching 90.degree. C. All Phadebas values are expressed relative to the value attained at the standard assay temperature of 55.degree. C. This value is considered to be 100% activity. This retention of greater than 50% of its Phadebas activity at temperatures approaching 90.degree. C. causes stickiness and gumminess in baked goods which have employed the Bacillus subtilis enzyme in the backing process.
One enzymatic approach to rearding bread staling is disclosed in U.S. Pat. No. 2,615,810 to Stone and involves the use of a heat-stable bacterial alpha-amylase enzyme to attack gelatinized starch granules during baking.
A refinement to Stone's approach is described in U.S. Pat. No. 4,299,848 to DeStefanis et al which discloses a process for the inactivation of the proteolytic enzymes present in commercially available heat stable bacterial alpha-amylase enzyme preparations obtained from extracts of Bacillus subtilis, Bacillus stearothermophilus or other microbial sources.
In a further refinement, U.S. Pat. No. 4,654,216 to Carroll et al discloses the addition of an enzyme mixture of heat stable bacterial alpha-amylase and a pullulanase to dough in proportions of from 0.25 to 5 SKB (alpha-amylase units) and 5 to 75 PUN (debranching enzyme units) per 100 grams of flour.
G. Bussiere et al in "The Utilization of Alpha-Amylase and Glucoamylase in Industrial Baking Technology", Annales De Technologie Agricole, volume 23 (2) pages 175 to 189 (1974) discloses studies on the role of heat stable bacterial alpha-amylases derived from Bacillus subtilis in bread making technology. Bussiere et al teaches that heat stable alpha-amylases of bacterial origin are effective in retarding staling, but produce a sticky bakery product when used at a dosage of 2.5 SKB units or more per 100 grams of flour.
A drawback of the Stone, DeStefanis et al, Carroll et al and Bussiere et al approaches is the tendency of heat stable bacterial alpha-amylases to remain active too long during baking and to cause gumminess in the finished product. As a result, these approaches require a degree of control over dosages and enzyme ratios which may be impractical to apply commercially.
An alternative to a heat stable bacterial alpha-amylase is described in Canadian Patent No. 980,703 to Grampp et al which discloses a thermolabile bacterial alpha-amylase without the gumminess causing characteristics of conventional bacterial alpha-amylases. However, Grampp et al does not disclose staling retardation and staling retardation would not be expected with this enzyme because of its thermolability. In terms of stability, the enzyme is similar to traditional fungal amylase which is most active at temperatures of 50.degree.-55.degree. C.
A bacterial alpha-amylase that is distinct from the aforementioned heat stable bacterial alpha-amylases and thermolabile alpha-amylase is derived from Bacillus megaterium available as strain NCIB, No. 11568 deposited in the National Collection of Industrial Bacteria, Aberdeen, Scotland. The gene coding for this enzyme has been inserted into plasmids. Microorganisms containing these plasmids and their use to obtain increased yields of the enzyme are disclosed in U.S. Pat. Nos. 4,469,791 and 4,806,426. This enzyme exhibits intermediate temperature stability in relation to the heat stable and thermolabile bacterial alpha-amylases. It is described in an article by David et al in Starch/Starke., Vol. 39, No. 12, pp. 436-440, (1987). However, the use of this enzyme in baked goods has not been heretofore disclosed.